Electrical coil

ABSTRACT

Strands of material along selected segments of an indeterminate length of stranded conductive material are welded together and severed to provide predetermined lengths of stranded conductive material having the strands at the ends thereof secured together to prevent unraveling. Such pieces of conductive material are secured to one or more coil lead wires to form a pair of terminal leads in a coil assembly. Each strand comprises a pliant fiber core about which is wrapped a conductive foil.

United States Patent inventor Roderick V. Sawyer Elkhart, Ind. Appl. No. 765,791 Filed Oct. 8, 1968 Patented May 18, 1971 Assignee CTS Corporation Elkhart, Ind.

ELECTRICAL COIL 5 Claims, 3 Drawing Figs. US. Cl 336/ 192, 339/275 Int. Cl H0lj 15/10 Field of Search 336/ 192; 339/275 (C) [56] References Cited UNITED STATES PATENTS 1,968,600- 7/1934 Driftmeyer 336/192 3,161,808 12/1964 Tromholt 336/192X Primary Examiner-E. A. Goldberg Attorneys-John J. Gaydos and Ralph E. Krisher, Jr.

ABSTRACT: Strands of material along selected segments of an indeterminate length of stranded conductive material are welded together and severed to provide predetermined lengths of stranded conductive material having the strands at the ends thereof secured together to prevent unraveling. Such pieces of conductive material are secured to one or more coil lead wires to form a pair of tenninal leads in a coil assembly. Each strand comprises a pliant fiber core about which is wrapped a conductive foil.

mtmwmmm 3579.166

l I -INVENTOR FIGURE-.3 RODERICK V. SAWYER BY WV A TORNE tors for interconnecting various component parts of such device or system. Generally, flexible conductors are needed when two or more components in a system must be free to move or vibrate relative to each other. In such a system, it is extremely desirable to use a flexible conductor that will not become brittle, crack, or be otherwise adversely affected by vibrations'imparted thereto. in electromechanical transducer systems, such as loudspeakers and some types of microphones, flexible conductors are used as a terminal lead to establish an electrical connection between a movable member or diaphragmand one or more other components that are designedto vibrate in rather precise modes relative to each other. In such systems it is desirable, if not necessary, that the flexible conductor exert a minimum amount of damping on the vibratory movement of the movable member. in addition, it is desirable for the flexible conductor to have an'extremely small mass so that the natural frequency of such system will not be substantially afl'ected because of the added mass of the conductor.

One material that has been found to be generally suitable for use as a flexible conductor in electromechanical transducers is comprised of a plurality of strands of electrically conductive material twisted together with each of the strands comprising a thin strip of conductive material wrapped around a lightweight cotton, linen, or synthetic material core. This material, commonly referred to as "tinsel," is relatively expensive but is used nonetheless because it is very supple and is characterized by a low mass per unit volume. In actual practice, however, pieces of stranded material are extremely difficult to handle and to connect with other materials because the individual strands in such material become unraveled at the ends thereof. This unraveling of individual strands has resulted in the waste of large amounts of material and has also been the cause of faulty connections between various electrical components. It has also been very difficult to provide automated systems for handling determinate lengths of stranded conductors because of the unraveling problem.

in the loudspeaker manufacturing art, the ends of relatively tine voice coil lead wires are normally connected to a piece of stranded conductor of determinate length. Suggested solutions for the unraveling problem have included the technique of manually wrappinga voice coil lead wire around one end of a stranded conductor and then soldering the stranded conductor and voice coil lead wire together. This technique, however, has been expensive in practice and has failed to solve the basic unraveling problem because many pieces of stranded conductor can still become unraveled before being connected to the voice coil lead wires and other pieces being connected to the voice coil lead wires and other pieces of stranded conductor can become unraveled during the operation of wrapping a voice coil lead wire around an end of each conductor. In addition, even when pieces of this material have been successfully handled without unraveling the strands at the ends thereof, the flexibility of the pieces of the material has often been impaired by the capillary flow of solder therealong during the soldering operation. The capillary flow of solder along a stranded conductor has also been one of the major problems encountered when molten solder has been applied to pieces of stranded conductive material either before or after pieces of stranded material have been severed from an indeterminate length of such material.

It will be appreciated, therefore, that it would be desirable to provide an improved stranded conductor wherein the inductors. Accordingly, it is an object of the present invention to provide a new and improved methodof making, from an indeterminate length of stranded conductive material, stranded conductors of any desired determinate length with the strands along the ends thereof restrained from unraveling. Another Object of the present invention is to provide a method of manufacturing pieces of stranded material having the individual strands at the ends thereof secured together. A more specific object of the present invention is to provide a method of making pieces of stranded conductive material and welding together the strands along the end portions thereof without deleteriously affecting the core of the material. A further object of the invention is to provide a new and improved method of making stranded conductors having a determinatev length wherein the strands at the ends thereof resist unraveling. Still another object of the present invention is to provide an improved stranded flexible conductor having the strands along the ends thereof welded together to prevent unraveling of the individual strands. A. still further object is toprovide an improved-coil assembly having aterminal'lead comprising a coil lead wire connected to a piece of flexible stranded conductive material along a welded portion thereof. Still another and more specific object of the invention is to provide an improved voice coil assembly wherein a voice coil lead wire is connected to a piece of flexible'stranded conductive material along a welded portion thereof. Further objects and advantages of the present invention will become apparent as the following description proceeds, and the features of novelty characterizing the invention will be pointed out with particularity in the claims annexed to and fon'ning a part of this specification.

Briefly, the present invention is concerned with an improved stranded flexible conductor and method of making the same. The stranded flexible conductor has the strands along the ends thereof welded together to prevent unraveling. Since the strands are welded, it is not necessary to'bond the strands together with an adhesive material and thereby increase the mass of the conductor. The welded end portions of the conductor are also less conducive to the capillary flow' of solder therealong than unwelded portions of the stranded conductor. When one or more pieces of conductive material are assembled with a pair of coil lead wires to form a pair of terminal leads in a coil assembly the welded end portions prevent the stranded conductive material from unraveling.

For a better understanding of the present invention, reference may be had to the accompanying drawings wherein: FIG. 1 illustrates a stranded conductor having the strands at one end thereof welded together in accord with the invention; FIG. 2 schematically represents the performance of the method of the invention; and FIG. 3 illustrates a coil assembly embodying the invention.

FIG. 1 illustrates a flexible stranded conductor 10 comprised of a plurality of strands 11-15 of conductive material such as silver-plated copper foil. Since it is desirable in many applications for the'conductor 10 to be very supple, each of the strands 11-15 are formed by wrapping foil around pliant cores 16 of material such as cotton. The end 17 of the conductor 10 is illustrated as being frayed with the strands therein unraveled as is frequently the case when the teachings of the present invention are not followed. The end 18 of the conductor 10 is illustrated with the strands therealong welded together to resist unraveling in accord with the invention.

According to the method schematically represented in FIG. 2, individual strands of material along selected segments of an indeterminate length of stranded conductive material are welded together and then severed to prevent the individual strands of conductive material from unraveling. The method may be carried out manually or by any suitable automatic means. In either event, the method of the present invention includes the steps of positioning a selected segment of an indeterminate length of stranded conductive material and welding means adjacent to each other, welding together individual strands of conductive material in the selected segment, and thereafter severing the indeterminate length of stranded material along the selected segment. The indeterminate length of material may bejmanually positioned adjacent to the weldand severing station 24, it being understood that the advancing means 22 includes any suitable'apparatus such as a pair of pinch rollers. When the conductive material 19 has been advanced a desiredamount the advancingmeans 22 dwells and v the individual strands along a segment of the material 19 are welded together at the welding station 23 when welding head 24, supported for reciprocativemovement relative to astationary welding support 26, moves toward thesupport 26 and vances the conductive material 19 past a weldingstati'on 23 compresses a segment 19a of material therebetween. When electrical potential is applied across a segment 19a of the cond'uctive material by a power supply means 27 such that a pulse iof welding current flows through the individual conductive strands of conductive material located between the welding head 24 and support 26. The power supply means 27 com- }prises any suitable circuitry and is connected to an electrode 1 portion 28 of the welding head and an electrode portion of the support through a conductor 29 and a not shown ground mm nector, respectively; When welding current is applied to the stranded conductive material I9, the strands thereof are fused :together and it is to be expressly understood that such fusing can be accomplished with welding electrodes positioned on radially opposite sides of the conductive material as illustrated in FIG. 2, or with electrodesspaced longitudinally along the 'conductive material. s t v Afterthe strands along a predetermined segment of conductive material have been welded together, the segment is severed. In FIG. 2, a severing means 24 is illustrated as including a table 3land a cutter 32 supported formovement toward and away from the table 31. By locating the cutter 32l-a distance from the welding station 23 equal to the distance the conductive material advances each time thatthe material ad 'vancing means 22 is actuated, the cutter 32 will automatically sever the stranded material along welded segments thereof. In

.view of the foregoing, it will be understood that byrepeatirig the steps of advancing, welding, and severing 'the stranded conductive material '19, a plurality of piecesof stranded con ductors having a predetermined length will be obtained having 'therealong.

minal leads 38, 39. The coil support in the form of a.bobbin 41 with acoil 42 of magnet wire would thereon and is particularly suitable for use as a voice coil assembly in an electromechanical transducer such as a loudspeaker. When molten'solder is used to reinforce the illustrated connection between the coil lead wires36, 37

wrapped around conductors 33, 34, the welded portions of the conductors provide the added advantage of inhibiting or retarding the capillary flow of solder andother wetting agents From-the foregoing description of the invention, it will be apparent that a new and improved method has been provided for making discrete pieces of stranded conductive material that retain a desired degree of flexibility, that have the strands at the ends thereof welded together to prevent'unraveling, and that may be economically handled in automated equipment without fraying the ends of the individual stranded conductors. It will also be apparent that stranded conductors embodying theinvention have, in addition to the above desirable charac eristics, the character st c of inhib ting the capillary flow of wetting agents therealong.

It will be understood that the particular embodiments of the invention described herein are intended as illustrative examples of the invention and that the invention is not necessarily limited to such embodiments. It will be understood therefore that other modifications of the invention described herein may be made, and that it is intended by the appended claims to cover all such modifications that fall within the true spirit and scope of the present invention.

Iclaim:

I. A coil assembly comprising a pair of stranded conductors having the individual strands along at least one of the ends of each of the conductors welded together to] prevent unraveling thereof, each of the individual strands comprising a pliant core of electrically nonconductive material and conductive foil wrapped around the .core,.and a winding of magnet wire having a pair of coil lead wires, each of said coil lead wires being connected to one of the stranded conductors. I

' 2. The coil assembly of claim 1, wherein the individual strands'are welded together along the interfaces thereof adjacent the ends of the conductors,-and the welded ends-of the stranded conductors inhibit the capillary flow of wetting agentstherealong. 3. The coil assembly of claim I, wherein the strands along both ends of each of the conductors are welded together and.

- the coil lead wires are each connected to the ends of the the individual strands along the ends thereof welded to prevent unraveling. a

In the coil assembly 32 of FIG. 3, a pair of flexible conductors 33, 34, having the individual strands of conductive material along the ends thereof welded together to prevent unraveling, are connected to coil lead wires 36, 37 to form ten stranded conductors. I

4. The coil assembly of claim I, wherein the coil assembly furthercomprises a coil support with the winding of magnet wire wound therearound.

5. The coil assembly of claim 4, wherein the coil lead wires are eachwrapped around the end of oneof the stranded conductors and'connected thereto, said coil assembly.

assembly 32 includes a winding 2 NITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 I 579 r Dated May 18, 1971 Roderick V. Sawyer It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In the Specification:

Column 1, line 57-58; Delete "being connected to the voice coil lead wires and other pieces".

Column 4, line 3; Change "would" to -wound-.

In the Claims:

Column 4, line 53; After "assembly" add comprising a voice coil assembly for an electromechanical tranducer.

Signed and sealed this 16th day of May 1972.

(SEAL) Abtest:

EDL'IARD I"I.FLETCI-ib;R,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents 

1. A coil assembly comprising a pair of stranded conductors having the individual strands along at least one of the ends of each of the conductors welded together to prevent unraveling thereof, each of the individual strands comprising a pliant core of electrically nonconductive material and conductive foil wrapped around the core, and a winding of magnet wire having a pair of coil lead wires, each of said coil lead wires being connected to one of the stranded conductors.
 2. The coil assembly of claim 1, wherein the individual strands are welded together along the interfaces thereof adjacent the ends of the conductors, and the welded ends of the stranded conductors inhibit the capillary flow of wetting agents therealong.
 3. The coil assembly of claim 1, wherein the strands along both ends of each of the conductors are welded together and the coil lead wires are each connected to the ends of the stranded conductors.
 4. The coil assembly of claim 1, wherein the coil assembly further comprises a coil support with the winding of magnet wire wound therearound.
 5. The coil assembly of claim 4, wherein the coil lead wires are each wrapped around the end of one of the stranded conductors and connected thereto, said coil assembly. 